Various types of power driven meat cutting tools have been devised wherein a ring blade is rotatably mounted on a blade holder which in turn is mounted on a manually manipulated power driven handle or handpiece. These tools have been used for some time to facilitate the removal of meat from a carcass primarily in a trimming operation, or for removing the meat remains from the bones. These meat cutting tools are either electrically or pneumatically driven. Some examples of the electrically driven prior art meat cutting tools are shown in U.S. Pat. Nos. 2,827,657; 3,024,532; 3,269,010; 4,324,043; 4,494,311 and 4,575,938.
These electrically driven meat trimming tools generally consist of a tubular handpiece formed of metal or plastic and having a hollow bore. An annular blade holder is attached to the front portion of the handpiece with a ring blade being removably mounted thereon by various mounting arrangements. The blade is formed with gear teeth extending about the top thereof, which teeth are in driving engagement with a pinion gear mounted within the end of the handpiece. The flexible metal drive shaft, one end of which is connected to an electric motor located adjacent to the work area, enters the rear of the handle and extends therethrough and terminates in a squared end. The squared end is engaged in a complementary-shaped opening in the rear of the pinion gear for rotatably driving the gear. Heretofore the flexible metal drive cable is surrounded by a flexible casing which terminates within an end of a hollow tubular shaped ferrule which is located within the handpiece, with the cable continuing through the ferrule into the pinion gear.
The usual operating speed of the electric drive motor and correspondingly of the drive shaft and rotatably mounted blade is approximately 3,450 rpm. The drive shaft is formed of one or more spiraled wires and is rotatably mounted with a drive shaft casing. The casing is formed of wrapped or wound wires of various cross sectional configurations which form a flexible yet strong casing or tubular housing for containing the rotating metal drive shaft. This metal casing then is covered with a thin film of plastic, preferably a reinforced polyethelene film having a thickness of approximately 4 mils, which subsequently is covered with an open mesh stainless steel wire braid. The braid then is covered by a coating of plastic preferably a food grade PVC material. The film prevents the penetration of the PVC through the braid and into the inner metal casing.
Although these prior art flexible drive shaft casings have performed satisfactorily, they possess certain inherent disadvantages and problems. The most serious problem is that the flexible drive shaft which is formed of metal, rotates at an extremely high rate of speed within the metal inner casing, and results in a metal-to-metal contact producing friction and heat. This metal-to-metal contact becomes especially critical when a high resistance force is applied to the rotating blade. For example when the operator digs the blade deep into the meat this places a large torque on the blade and correspondingly on the drive shaft. This torque causes the drive shaft to spiral or form a sine wave configuration within its metal casing causing contact areas with the casing resulting in "hot spots" developing between the casing and shaft. These contact areas shorten the life of both the shaft and casing requiring periodic replacement of one or both of the components. This excessive rubbing or contact between the shaft and casing quickly wears away the galvanizing coating which is formed on the inside surface of the metal casing. The metal casing must be galvanized since it is subjected to continuous wet and damp conditions in a meat trimming plant and must be continually washed and cleaned since the equipment is in contact with the meat. These worn areas then become subject to rapid rusting which provides a further abrasive action against the rotating cable accelerating the destruction of the cable and casing. Also upon the torque becoming too great, the drive shaft will "lock up" within the protective metal casing due to the spiraling effect of the shaft. The inner metal casing also increases the weight of the casing assembly and is relatively stiff requiring greater effort on the part of the operator when moving the knife across the carcass increasing operator fatigue after extended periods of use during a usual work shift.
Therefore, the need has existed for an improved flexible drive shaft casing of the type intended primarily for use with the flexible drive shaft of a meat trimming knife which eliminates the above described problems.